In the following description, texts, phrases, or words in Japanese including Japanese characters will be explained with reference to FIG. 17. In FIG. 17, pronunciations of each of the texts, phrases, and words will be shown by Roman alphabets in parenthesis.
A system of synthesizing a voice from text adopts a function of assigning a higher priority to the user-registered words additionally registered by the system user than the system words previously registered in the system in the speech synthesis. For example, if the system user adds a user-registered word of C1 as shown in FIG. 17 to the system, while a system word of C2 is registered in the system, later the system will synthesize a voice with the pronunciation of C1 taking precedence over the pronunciation of C2.
In a language like Japanese in which written words are not described separately, however, if text contains a user-registered word added by the system user at the stage of solid writing, there is a possibility that a word sequence not containing the word corresponding to the user-registered word may be generated in the process of morphological analysis. For example, assume that the system user registers text of C3 as shown in FIG. 17 as user-registered words expecting that the part C4 in the text C3 will be output as reading of C1. However, if a written text that are described separately as C5 is generated in the process of morphological analysis, a space is placed between C4 and C6 and therefore reading of C1 is not output (instead, reading of C2 should be output). In contrast, if text contains an undesirable word for the system user such as a forbidden word in broadcast domain (a word which is not allowed to be used on a broadcast), a technique of detecting a word matching a forbidden word in broadcast domain contained in a list after the word sequence is determined according to morphological analysis and then skipping the word matching the forbidden word in broadcast domain or replacing the word with another word is proposed. (For example, refer to JP-A-5-165486.) However, a system of preventing generation of a word sequence containing an undesirable word for the system user before determining a written text that are described separately does not exist.
The same problem still exists in a language in which a space is left between words (the language in which written text are described separately). Although a word boundary is clear, if the strength of concatenation of the preceding and following words is evaluated in morphological analysis for determining a word sequence, even if a word is registered as the user-registered word, the word sequence containing the word corresponding to the user-registered word is not necessarily generated.